14. Downloading free mobile apps
Free generally means "stuffed with malware", "impossible to play without paying real cash money" or "full-screen video ads! Just what everyone wants!" Not all apps are like that, of course, but the good ones get bought by Facebook or Flipboard as soon as you start to rely on them.
15. Accepting friend requests from ancient mates
Remember them as they were, not as the bigots they've apparently all become.
16. Thinking a cheap printer is a good investment
Cheap printers are only cheap until you get them home. Their ink reservoirs are smaller than ants' bladders, they jam more often than Beyonce's backing band and the ink they use is pricier than plutonium.
17. Looking at anything at all online
Ad networks know what you're looking at, and they'll never let you forget about it. We looked at a shed in 1996, and our internet has been full of sheds ever since. And by sheds, we mean bras.
18. Buying BlackBerry
According to analysts at Kantar Worldpanel ComTech, BlackBerry's European market share is down from last year's 3.4% to a barely-there 1.5%. This is not a platform whose best days are ahead of it.
19. Buying a phone running old-Android
There are two kinds of old-Android buyers: there are the people who don't care which version they have, and there are the people who bought a device expecting the manufacturer or network to provide a firmware update. The second lot are easy to spot, because they're crying.
20. Selling your old kit on ebay
Goodbye, kit! Goodbye, money!
21. Choosing car firms' in-car tech
Adding in-car entertainment and navigation to new cars can add thousands to the bill, but two years down the line the maps are out of date, the storage is stuffed and the iPod connector doesn't work because Apple's dumped the design. Proprietary in-car tech has a limited lifespan, but incoming systems such as Apple CarPlay don't: when you upgrade your phone, you upgrade your car tech too.
22. Keeping files in the wrong formats
If you're transcoding video, ripping music or storing anything for future safekeeping, make sure it's in a format you'll still be able to access years from now, not a format whose continued existence or copy protection system depends on the continued goodwill of a handful of companies (or worse, a single company).
23. Using social media after a few drinks
"I know, I'll pick a fight with Piers Morgan!"
24. Letting kids anywhere near your game discs
Jammy-fingered disc destruction just means a trip to the torrents when it's a CD or DVD, but a gubbed games disc means buying a fifty-quid game all over again. That and Barney the Dinosaur are very good reasons not to have children.
25. Early adoption of anything
Early adoption is rather like travelling during the school holidays or going to London: everything's horrible and costs a fortune.
Whether it's an iPhone or an Xbox One, if you're a day-one queuer you're paying a hefty price for bragging rights.